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INTERDISCIPLINARY JOURNAL OF CONTEMPORARY RESEARCH IN BUSINESS
JUNE 2011
VOL 3, NO 2
decisions) occurred when reducing the buffer size further caused a deterioration in significant
metrics or when the buffer size equaled one Overall pull system implementation stages have
been said to be .
• process improvements;
• group technology layout
• pull system scheduling;
• cell operations stopping with any cell equipment failure (cell down rule).
An example first state of the process improvements stage would be applying process
improvements to the first process, perhaps improving the screen printing process. The second
state for the process improvement stage would then be improving the second process. Example
states within the stage of group technology (GT) layout may be the number of cells developed.
For example, the first state in the GT layout stage may have only one cell, while the second state
of the GT stage may have two or three cells.
5. Pull system implementation
The simulation model was revised for each of the four major pull system implementation
stages. Process improvements, the first implementation stage, included reducing process times,
inspection times and the number of defects to a level thought realistic by engineers familiar with
the system. In an actual manufacturing facility, process changes could be made continually.
Implementing a group technology layout was the next stage. Machines to be grouped into cells
were selected by their criticality to the process, original location and number of duplicate
equipment .First, four cells were formed in the A/I area. Next, two cells were created in the SMT
area.
The third implementation stage was pull system scheduling. A simple Kanban system was
integrated process-by-process working backward from final inspection. The fourth and last pull
system implementation stage was the rule of stopping all cell operations when any of that cell's
equipment broke down (cell down rule). The enforcement of the cell down rule is similar to
having a buffer of zero within the cells. This strict rule must be implemented last because of its
dependence on high quality, high machine reliability and balanced smooth production flow
.Global variable toggles were placed in the simulation model to stop a given cell's operations
when any of that cell's machines broke down. A part loaded on a machine at the time of machine
failure was assumed to be destroyed.
Implementation stages were layered, i.e. pull scheduling was integrated into a group technology
model. One simulation model was run for each of the manager-recommended buffer sizes from
one to five, for the critical processes, for each implementation stage. When the last major pull
system implementation stage was reached and further buffer size changes in that stage did not
result in significant metrics improvement, the transition endpoint was said to be reached Without
substantial process enhancement, additional significant performance measure improvement was
assumed not to be possible after reaching complete pull system implementation. When a saddle
point or inflection point was reached the buffer size associated with the minimum system run
time was chosen Buffer size changes from five to one did not significantly impact the quality
performance measure for the first three pull system implementation stages. When the cell down
rule was added to the installed protocol of pull scheduling, quality became sensitive to buffer
size.IR reflow and wave solder, involving fewer non cellular machines, did not show this
sensitivity to buffer size. In this case, cellular grouping seemed to decrease the sensitivity of
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